Ultrasonic cleaning apparatus

1. An ultrasonic cleaning apparatus comprising: a cleaning tank filled with a cleaning liquid; a thin plate member holder for holding a thin plate in said cleaning liquid, said holder having groove supporting members for supporting in at least two places the lower periphery of the thin plate member, said supporting members being provided at different height positions; and ultrasonic wave generating means for radiating ultrasonic waves parallel with a cleaning face of said plate member, said generating means comprising a generator on two opposite sides of the plate member holder, each generator being provided with an ultrasonic protection plate movable between a position in front of the generator and a retracted position so that when the generator is operating, the plate is in a retracted position and when the generator is not operating, the plate is in front of the generator.

2. An ultrasonic cleaning apparatus according to claim 1, wherein the upper part of each member forming said thin plate member holder tapered in cross-section.

3. An ultrasonic cleaning apparatus according to claim 1, wherein an upper part of each member forming said thin plate member holder is semi-circular in cross-section.

4. An ultrasonic cleaning apparatus according to claim 1, wherein said means comprises the supporting members being provided at different height positions, and said generators being on two opposite sides of the plate member.

5. An ultrasonic cleaning apparatus according to claim 4, wherein said generators are offset relative to one another, and said means further includes means for shifting the plate member holder in said cleaning liquid.

6. An ultrasonic cleaning apparatus according to claim 4, wherein the upper part of each member forming said thin plate member holder is tapered in cross-section.